The proposed area of investigation will involve studies of bone marrow transplantation. The research is divided into four projects encompassing: 1. Clinical Trials: a. Acute Leukemia. b. Aplastic Anemia. c. Autologous Bone Marrow Transplantation. 2. Immunobiology of Bone Marrow Transplantation: a. Graft Rejection. b. Graft-versus-Host Disease (GvHD). c. Post-transplant Immunodeficiency. 3. Interstitial Pneumonitis. 4. Infectious Disease Complications of Bone Marrow Transplantation.